/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.calcite.runtime.variant;

import org.apache.calcite.runtime.rtti.RuntimeTypeInformation;

import org.checkerframework.checker.nullness.qual.Nullable;

/** The VARIANT type has its own notion of null, which is
 * different from the SQL NULL value.  For example, two variant nulls are equal
 * with each other.  This class represents such values. */
public class VariantNull extends VariantValue {
  // Protected constructor to enforce a singleton pattern
  protected VariantNull() {}

  @Override public String getTypeString() {
    return "VARIANT";
  }

  @Override public @Nullable Object cast(RuntimeTypeInformation type) {
    // Result is always null
    return null;
  }

  @Override public @Nullable Object item(Object index) {
    // Result is always null
    return null;
  }

  public static final VariantNull INSTANCE = new VariantNull();

  /** Get the single instance of this type. */
  // Called from BuiltInMethod.VARIANTNULL
  public static VariantNull getInstance() {
    return INSTANCE;
  }

  @Override public int hashCode() {
    return 0;
  }

  @SuppressWarnings("EqualsWhichDoesntCheckParameterClass")
  @Override public boolean equals(@Nullable Object other) {
    return other == INSTANCE;
  }

  @Override public String toString() {
    return "null";
  }
}
